[Feature]: Keep launcher view visible whenever a tab has no blocks

[dvictor357]

Feature description

Currently, when I close the last block in a tab, Wave closes the entire tab instead of keeping it
open and showing the launcher (“Type to Filter, Enter to Launch, Arrow Keys to Navigate”).

There is one exception: if a Wave AI block is open and I close all the other blocks, the launcher
view appears behind it. This is the behavior I’d like to see consistently whenever there are no
blocks in a tab.

Requested behavior:

• A tab should remain open even after the last block is closed.
• Whenever a tab has zero blocks, it should automatically show the launcher/placeholder widget
  (the same “Type to Filter, Enter to Launch, Arrow Keys to Navigate” view).
• This launcher state should be treated as the default “empty tab” view, regardless of what types
  of blocks were previously open.

Rationale:

• Keeps the tab as a persistent workspace instead of destroying it when empty.
• Makes it faster to launch new widgets in the same tab after clearing out old ones.
• Aligns the behavior with the existing Wave AI case, where the launcher is already visible behind
  the AI block when other blocks are closed.

Implementation Suggestion

No response

Anything else?

No response